When the album sidecar location isn't writable (e.g. read-only music
mount in a container), the album-cover write previously failed and
left cover_art_source NULL forever — every scan retried the same
provider call and re-failed at the same os.WriteFile. With a managed
data_dir available, we fall back to <DataDir>/album-art/<album_id>/
cover.jpg and record that path on the album row. The cover-serving
HTTP path already serves whatever cover_art_path stores, so the
client sees the art uniformly regardless of where it landed.
DataDir is opt-in via the Enricher field (cmd/minstrel/main.go sets
it from cfg.Storage.DataDir on the production path; tests leave it
empty and behave as before).
bvandeusen
bd4f5d3818